<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>

</head>
<body>
<div id="id1">

</div>

<script>
  'use strict';
  var id1 = document.getElementById("id1");
  id1.innerText='123';
  id1.innerHTML='<strong>strong</strong>';
  id1.style.color="red";
  id1.style.padding="10px";
  id1.style.fontSize='50px';
</script>

</body>
</html>